Numerous production plants, including various refineries, gas plants, upgrading plants, and gasification plants include sulfur recovery units (SRU) that produce liquid sulfur, which is typically in an un-degassed form and often contains 200 to 350 ppmw H2S. If the liquid sulfur is not degassed, H2S will be released during storage, handling, loading, and/or transport, which can create an explosive mixture of H2S in air. Moreover, H2S poses a toxicity hazard as well as a noxious odor problem when released from the un-degassed liquid or solid sulfur.
To manage the H2S release, various methods and systems are known in the art, including collection of the H2S via vents. However, such collection typically requires ejectors or blowers for routing the collected H2S to an appropriate location, which adds significant capital and/or operating expense. To avoid H2S release from vent gases, vents from un-degassed sulfur loading can be routed to an incinerator. Unfortunately, such routing increases the SO2 emissions to the atmosphere and is also less than desirable. Where larger volumes of degassing must be handled (e.g., in-pit degassing), vented streams have been routed to a sulfur recovery unit (SRU) main burner or reaction furnace chamber (mRF) via long runs of jacketed piping. A typical example for such configuration is shown in U.S. Pat. No. 4,478,811, and a somewhat similar system is shown in U.S. Pat. App. No. 2002/0159938. Unfortunately, such large vent volumes often cause problems with combustion air control in the SRU and insufficient furnace temperature, as well as corrosion and plugging of piping. These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
In still other known methods and systems, sulfur rundown pits (or vessels) are swept with air. While such sweep is conceptually simple, vent gases cannot be routed to the hydrogenation reactor (or associated heater/reducing gas generator (RGG)) as the oxygen in the vent gas tends to poison the hydrogenation catalyst. Additionally, it is difficult to collect vents from loading arms (e.g., truck, rail, or ship) as they are often not located nearby the SRU or any incinerator, or catalytic or thermal oxidizer. Similarly, storage tanks may also be remotely located and thus compound difficulties with routing sulfur-containing vent gases.
Further known methods of management of vent gases are described, for example, in WO 97/10174 where liquid sulfur is degassed in separate and serially arranged compartments. Here, a stream of finely divided oxygen-containing gas is combined under agitation with the liquid sulfur to reduce residual sulfide/polysulfide concentration. Unfortunately, while such methods is at least conceptually effective, significant material and complexity is required. Similar problems are encountered in WO 95/06616 where liquid sulfur is treated with stripping gas using a shroud and impeller. In further systems and methods, as for example, shown in U.S. Pat. No. 7,927,577, liquid jet pumps or eductors use a pumped liquid sulfur recycle stream as a motive fluid to boost sulfur rundown pressure and so provide entrainment and enough agitation in the liquid sulfur such that simultaneously degassing occurs within the sulfur collection piping and associated systems. However, such systems often add equipment costs and complexity.
In still further known systems, sulfur is degassed outside of a rundown pit using an oxidizing gas at elevated pressure as described in WO 02/088023. The so obtained waste gas is then used as a motive fluid in an eductor that carries sweep gas from the sulfur rundown pit. As used herein, the terms “rundown pit” and “vessel” when used in conjunction with collection of liquid sulfur are used interchangeably herein and refer to a containment that receives liquid sulfur from a sulfur producing process, most typically via a sulfur condenser. While such configurations and methods advantageously improve at least some of the operational parameters, several drawbacks nevertheless remain. Most significantly, where the waste gas and the sweep gas are fed to the SRU, operation of the SRU is often adversely affected. To avoid such drawbacks, the waste gas and sweep gas can be fed to an oxidizer. However, such treatment leads to the production of sulfur oxides, which have to be appropriately dealt with.
Thus, even though there are various systems and methods for sulfur-containing vent gas treatment known in the art, all or almost all of them suffer from one or more disadvantages. Therefore, there is still a need for improved configurations and methods of treatment of sulfur-containing vent gases.